The present invention relates to novel water soluble condensation products of methylol phosphorus compounds with nitrogen compounds, to the processes of using these water soluble materials to produce flame-retardant textile materials and to the flame-retardant textile materials so produced.
The practice of treating textile materials for flame retardance has assumed increasing importance with the adoption of federal, state and municipal legislation designed to protect the public from unreasonable hazards of flammable textile products.
The compound tetrakis(hydroxymethyl) phosphonium chloride is known to be a basis for flame-retardant finishes for cellulosic fabrics. Reeves and Guthrie in U.S. Pat. No. 2,809,941 used a solution of tetrakis(hydroxymethyl)phosphonium chloride, melamine-formaldehyde resin and urea to treat cotton fabrics by a pad-dry-cure method. This treatment and slight modifications of it have been used commercially to give cotton fabrics flame-retardance durable to multiple launderings. The treatment, however, causes high fabric strength losses and makes the fabrics too stiff to use except for certain areas such as industrial cotton work clothing and tent liners.
Reeves and Guthrie in their later-filed U.S. Pat. No. 2,772,188 disclosed an improved process for forming an insoluble polymer of tetrakis(hydroxymethyl)phosphonium chloride in cellulosic fabrics by what is known as a chemical cure. In water there was made a pre-polymer of tetrakis(hydroxymethyl)phosphonium chloride and either methylolmelamine or urea or phloroglucinol. This solution was padded onto cotton fabric. The fabric was dried and then treated with ammonia (chemical cure) to produce an insoluble polymer in and on the fabric. The fabric was fire retardant.
Coates in U.S. Pat. No. 2,983,623 improved on this process by using a chemical cure which consisted of treating impregnated fabric first with gaseous ammonia and then with aqueous NH.sub.3. Pre-condensates were made by refluxing tetrakis(hydroxymethyl) phosphonium chloride in water containing either urea, melamine, a urea and thiourea mixture, dicyandiamide or guanidine. Water solutions of the pre-condensate were padded onto cotton fabric. The fabric was dried and subsequently put first into a gaseous ammonia chamber and then into an aqueous solution of ammonia to form an insoluble polymer in and on the fabric. This fabric was flame-retardant. The particular process using a tetrakis(hydroxymethyl)phosphonium chloride-urea pre-condensate has become commercial and is known as the "Proban" process. It is adequate for cellulosic textiles, but is not satisfactory for polyester-cotton blend fabrics.
Coates and Chalkey in U.S. Pat. No. 3,236,676 further simplified the process by using tetrakis(hydroxymethyl)phosphonium salts (abbreviated THP salts) neutralized with a base such as NaOH to a pH between 3 and 9.5 instead of the tetrakis(hydroxymethyl)phosphonium chloride-urea precondensate. Fabric was padded with the neutralized THP salt, dried and given a heat cure sufficient to fix the THP salt on the fabric. Subsequently the fabric was treated with ammonia to form an insoluble polymer in and on the fabric.
Beninate et al. in U.S. Pat. No. 3,607,356 improved on this process by omitting the heat cure to fix the THP salt prior to the treatment with gaseous ammonia. They neutralized THP salt with a base such as NaOH to a pH of about 7.5 to 7.9. They called this neutralized product THPOH. In reality a solution of THP salt neutralized in this way consists mostly of tris(hydroxymethyl)phosphine (Reeves et al., Textile Chemist and Colorist 2, 283-285 (1970)). Cotton fabric was padded with an aqueous solution of this "THPOH" and dried to a moisture content of about the normal cotton moisture regain, or a little higher. This fabric was then subjected to an atmosphere of dry, gaseous ammonia to form an insoluble polymer in and on the fabric. They claimed this process would give flame-retardance not only to cellulosic fabrics and wool but also to polyester-cotton blends. This process has been commercialized and is adequate for cotton fabrics, but does not give adequate flame-retardance to a polyester-cotton blend containing more than 20% polyester.
LeBlanc and Gray (Textile Chemist and Colorist 3, 263-265 (1971)) did a study on the application of THPOH finish to polyester-cotton blends. They found that it is possible to give a minimum level of fire-retardance to blends which have no more than 12.5-25% polyester. Even at these levels of polyester, the treated fabrics were excessively stiffened by the treatment.
Tesoro (Textile Chemist and Colorist 5, 235-238 (1973) and NTIS-COM-73-11265) concluded that a satisfactory flame-retardant system for polyester-cotton should contain phosphorus and bromine and that the presence of nitrogen is not important.
Ciba-Geigy Corporation has disclosed developmental product, Pyrovatex 3762, for making polyester-cotton blends flame retardant (John Leddy and Rene Eckert, "Durable Flame Retardant Finishing of Cotton and Polyester-Cotton Blends", Proceedings of the 1973 Symposium on Textile Flammability, LeBlanc Research Corporation, East Greenwich, R.I.) From German Specification DOS 2,136,407 it appears the product, a "phosphonium oligomer" is a water-soluble self-condensation product of tetrakis(hydroxymethyl)phosphonium chloride. It can be applied to polyester-cotton blends by a pad-dry-cure-afterwash process. The padding solution contains the self-condensation product Pyrovatex 3762, a dimethylolmelamine, urea, a softener and a wetting agent. The Pyrovatex 3762 has a highly objectionable phosphine-type odor during fabric processing and the processed fabrics are very stiff.
In British Pat. No. 761,985 ammonia is condensed with a THP salt but the product is a water-insoluble polymeric solid and is employed to treat cellulosic material as an emulsion in water.
In Chemical Abstracts Vol. 79 (1973) 20256x there is abstracted German DOS 2,242,681 which self-condenses tetrakis(hydroxymethyl)phosphonium chloride to remove water and leave a polymer which, with urea, forms a dispersible material for addition to viscose spinning dopes. In Chemical Abstracts Vol. 79 (1973) 20258z there is abstracted German DOS 2,242,682 wherein THPC is condensed with an amine such as dodecylamine in xylene to give a condensate. In Chemical Abstracts Vol. 79 (1973) 93383w there is abstracted German DOS 2,255,113 wherein THPC is simultaneously reacted with ammonia and urea. None of these treatments, however, is believed to be commericial.
Thus, while 50--50 or 65-35 polyester-cotton blend fabrics comprise about one-third of the total textile fabrics currently produced in the United States, at the present time there is no commercially available finish for flame-retarding such polyester-cotton blends. One of the problems is that the polyester polymer fiber has no reactive groups on it such as the hydroxyl groups on the cellulose polymer. When the polyester content of a fabric approaches 50%, the number of available hydroxyl groups on the fabric is decreased to such an extent that it becomes difficult to attach flame-retardant compounds onto the fabric. While Pyrovatex 3762 has more reactive methylol groups per molecule than do THP salts so that it can be polymerized with a resin such as dimethylolmelamine with a higher efficiency than THP salts, its disadvantages have been outlined hereinabove.